Semiconductor device and manufacturing method thereof

ABSTRACT

Provided is a flexible device with fewer defects caused by a crack or a flexible device having high productivity. A semiconductor device including: a display portion over a flexible substrate, including a transistor and a display element; a semiconductor layer surrounding the display portion; and an insulating layer over the transistor and the semiconductor layer. When seen in a direction perpendicular to a surface of the flexible substrate, an end portion of the substrate is substantially aligned with an end portion of the semiconductor layer, and an end portion of the insulating layer is positioned over the semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device.

The “semiconductor device” in this specification and the like means alldevices that can operate by utilizing semiconductor characteristics.Accordingly, a transistor, a semiconductor element, a semiconductorcircuit, a memory device, an imaging device, an electro-optical device,a power generation device (e.g., a thin film solar cell and an organicthin film solar cell), an electronic device, and the like are includedin the category of the semiconductor device.

2. Description of the Related Art

In recent years, a flexible device in which a semiconductor element, alight-emitting element, and the like are provided over a flexiblesubstrate has been developed. Typical examples of the flexible deviceinclude, as well as a lighting device and an image display device, avariety of semiconductor circuits including a semiconductor element suchas a transistor.

As a method of manufacturing a semiconductor device including a flexiblesubstrate, a technique has been developed in which a semiconductorelement such as a thin film transistor is formed over a supportsubstrate (e.g., a glass substrate or a quartz substrate), and then thesemiconductor element is transferred to a flexible substrate. Thistechnique needs a step of separating a layer including the semiconductorelement from the support substrate.

For example, Patent Document 1 discloses a peeling technique using laserablation as follows. A separation layer formed of amorphous silicon orthe like is formed over a substrate, a layer to be peeled is formed overthe separation layer, and the peeled layer is bonded to a transfer bodywith a bonding layer. The separation layer is ablated by laserirradiation, so that peeling occurs in the separation layer.

Patent Document 2 discloses a peeling technique as follows. A metallayer is formed between a substrate and an oxide layer and peeling isperformed at the interface between the oxide layer and the metal layerby utilizing weak bonding at the interface, so that a layer to be peeledand the substrate are separated from each other.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. H10-125931

[Patent Document 2] Japanese Published Patent Application No.2003-174153

SUMMARY OF THE INVENTION

In the case where peeling is performed between a peeling layer providedover a substrate and a layer to be peeled (hereinafter referred to aslayer) formed over the peeling layer, a stack formed of thin films(e.g., the layer, a thin film transistor (TFT), a wiring, and aninterlayer film) is provided over the peeling layer. The stack has athickness of several micrometers or less and is very fragile. Whenpeeling is performed between the peeling layer and the layer, a highbending stress is applied to an end portion of the layer (a peelingstarting point); as a result, breaking or cracking (hereinafter,collectively referred to as crack) easily occurs in the layer. Moreover,when such a crack develops from the end portion of the layer into asemiconductor element or a light-emitting element, these elements mightbe broken.

To improve productivity of flexible devices, it is preferable that aplurality of devices be manufactured at a time over a large substrateand the substrate be divided with a scriber or the like. This stepcauses a problem in that a crack occurs in or develops from an endportion of the substrate due to stress applied when the substrate isdivided.

In view of the above, an object of one embodiment of the presentinvention is to provide a flexible device with fewer defects caused by acrack. Another object is to provide a flexible device having highproductivity.

Note that in one embodiment of the present invention, there is no needto achieve all the objects. The description of these objects does notdisturb the existence of other objects. Other objects will be apparentfrom and can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a semiconductor deviceincluding: a display portion over a flexible substrate, including atransistor and a display element; a semiconductor layer surrounding thedisplay portion; and an insulating layer over the transistor and thesemiconductor layer. When seen in a direction perpendicular to a surfaceof the flexible substrate, an end portion of the substrate issubstantially aligned with an end portion of the semiconductor layer,and an end portion of the insulating layer is positioned over thesemiconductor layer.

In the semiconductor device with the above structure, the semiconductorlayer preferably contains the same material as a semiconductor in achannel of the transistor.

In the semiconductor device with the above structure, it is preferablethat a conductive layer surrounding the display portion be furtherincluded between the display portion and the semiconductor layer.

In the semiconductor device with the above structure, the conductivelayer preferably contains the same material as a gate electrode, asource electrode, or a drain electrode of the transistor.

Another embodiment of the present invention is a method of manufacturinga semiconductor device, including the steps of: forming a peeling layerover a support substrate; forming a layer over the peeling layer;forming, over the layer, a transistor and a semiconductor layersurrounding the transistor; forming, over the transistor and thesemiconductor layer, an insulating layer with an opening over thesemiconductor layer; separating the peeling layer and the supportsubstrate from the layer; bonding a flexible substrate to a separatedsurface of the layer; and cutting the flexible substrate, the layer, andthe semiconductor layer in a position overlapping with the opening.

In this specification and the like, the expression that an end portionof a layer is “substantially aligned” with an end portion of anotherlayer includes the case where the end portions of the layers do notcompletely overlap with each other (needless to say, the expressionincludes the case where the end portions of the layers completelyoverlap with each other); for example, an end portion of an upper layermay be positioned on an inner side than an end portion of a lower layer,or may be positioned on an outer side than the end portion of the lowerlayer.

The present invention can provide a flexible device with fewer defectscaused by a crack or a flexible device having high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a structural example of a display device inEmbodiment.

FIGS. 2A and 2B illustrate a structural example of a display device inEmbodiment.

FIGS. 3A and 3B illustrate a structural example of a display device inEmbodiment.

FIGS. 4A to 4D illustrate a method of manufacturing a display device inEmbodiment.

FIGS. 5A to 5C illustrate the method of manufacturing the display devicein Embodiment.

FIGS. 6A and 6B illustrate the method of manufacturing the displaydevice in Embodiment.

FIG. 7 illustrates a structural example of a display device inEmbodiment.

FIGS. 8A to 8C illustrate structure examples of electronic devices inEmbodiment.

FIGS. 9A and 9B are an optical micrograph of a sample and a crosssectional view of the sample in Example.

FIGS. 10A and 10B are an optical micrograph of a sample and a crosssectional view of the sample in Example.

FIGS. 11A and 11B are an optical micrograph of a sample and a crosssectional view of the sample in Example.

FIGS. 12A and 12B are an optical micrograph of a sample and a crosssectional view of the sample in Example.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe description below, and it is easily understood by those skilled inthe art that various changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be construed as being limited to thedescription in the following embodiments.

Note that in the structures of the present invention to be describedbelow, the same portions or portions having similar functions aredenoted by the same reference numerals in different drawings, anddescription of such portions will not be repeated. Further, the samehatching pattern is applied to portions having similar functions, andthe portions are not especially denoted by reference numerals in somecases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, the scale of each structure is notnecessarily limited to that illustrated in the drawings.

Note that in this specification and the like, ordinal numbers such as“first”, “second”, and the like are used in order to avoid confusionamong components and do not limit the number.

Embodiment 1

In this embodiment, a structure and a manufacturing method of an imagedisplay device, which is an example of a semiconductor device of oneembodiment of the present invention, are described with reference todrawings. As an example of the image display device, an image displaydevice (hereinafter, also referred to as display device) including anorganic EL element is described below.

Note that in this specification and the like, the display device mayinclude any of the following modules in its category: a module in whicha connector such as a flexible printed circuit (FPC) or a tape carrierpackage (TCP) is attached to a display device; a module having a TCPprovided with a printed wiring board at the end thereof; a module havingan integrated circuit (IC) directly mounted over a substrate over whicha display element is formed by a chip on glass (COG) method; a module inwhich a touch sensor is mounted.

[Structural Example of Display Device]

FIG. 1A is a schematic top view of a display device 100 with a topemission structure. Note that in FIG. 1A, some components are notillustrated for clarity.

The display device 100 includes, over a flexible substrate 101, adisplay portion 102; a signal line driver circuit 103; a scan linedriver circuit 104; and an external connection terminal 105 electricallyconnected to these elements. For example, an FPC or an IC can be mountedon the external connection terminal 105, and via these elements, asignal such as a power supply potential and a driving signal can beinput to the display portion 102, the signal line driver circuit 103,and the scan line driver circuit 104.

Here, a semiconductor layer 110 is provided in an end portion of thesubstrate 101 to surround the display portion 102. The semiconductorlayer 110 is provided over and along a periphery of the substrate 101.

A conductive layer 120 is provided between the semiconductor layer 110and the display portion 102 to surround the display portion 102.

FIG. 1B is a schematic cross-sectional view taken along the lines A-B,C-D, and E-F in FIG. 1A. The line A-B cuts a region including the endportion of the substrate 101, the external connection terminal 105, andthe signal line driver circuit 103. The line C-D cuts a region includingthe display portion 102. The line E-F cuts a region including anopposite end portion of the substrate 101.

In the display device 100, a layer 112 to be peeled (hereinafterreferred to as layer 112) is provided over the flexible substrate 101with a bonding layer 111 positioned therebetween. A light-emittingelement 124 functioning as a display element; a transistor which arecomponents of the display portion 102, the signal line driver circuit103, the scan line driver circuit 104, or the like; the externalconnection terminal 105; the semiconductor layer 110; the conductivelayer 120; and the like are provided over the layer 112.

The structure of the display device 100 is suitable for obtaining aplurality of devices from one substrate in such a manner that aplurality of display devices 100 is manufactured at a time over onesubstrate, and then the substrate is divided for separating theplurality of display devices 100. FIG. 2A is a schematic top viewshowing a state after four display devices 100 are manufactured at atime over a substrate and before the substrate is divided. FIG. 2B is aschematic cross-sectional view taken along the lines G-B, C-D, and E-Hin FIG. 2A.

FIG. 2A shows the case where four display devices 100 are arranged (in a2×2 matrix). Arrangement of the display devices 100 (e.g., the directionand the number of display devices 100) is not limited to the above.Arrangement by which as many display devices 100 as possible can bearrayed is employed depending on the substrate size, the area of eachdisplay device 100, and the like.

The display portion 102 in each display device 100 is surrounded by thesemiconductor layer 110. That is, there is at least one semiconductorlayer 110 between two adjacent display devices 100. When the substrateprovided with the display devices 100 is divided for separating thedevices, a cut portion 140 overlaps with the semiconductor layer 110.

Openings are formed in insulating layers (e.g., insulating layers 134,135, 136, and 137) over at least the transistor such that a top surfaceof the semiconductor layer 110 is partly exposed. In FIGS. 1A and 1B andFIGS. 2A and 2B, the openings are also formed in an insulating layer 138that is over the semiconductor layer 110 and functions as a gateinsulating layer of the transistor.

Thus, in the state where the substrate 101 is divided (FIGS. 1A and 1B),the openings overlap with the end portions (end faces) of the substrate101. The division is performed in a region overlapping with thesemiconductor layer 110, so that an end portion (end face) of thedivided semiconductor layer 110 is substantially aligned with an endportion (end face) of the substrate 101. In other words, when seen in adirection perpendicular to a surface of the substrate 101, an endportion of the substrate 101 is substantially aligned with an endportion of the semiconductor layer 110, and an end portion of theinsulating layer is positioned over the semiconductor layer 110.

With this structure in which the semiconductor layer 110 is not coveredwith an insulating layer in the cut portion 140, occurrence ordevelopment of a crack in the insulating layer can be effectivelyprevented when pressure is applied thereto by the substrate division. Inmany cases, a crack is less likely to occur or develop in asemiconductor layer than in an insulating layer; therefore, part of thesemiconductor layer 110 is on the outermost surface in the cut portion140; thus, occurrence of a crack can be effectively reduced.

The process of manufacturing the display device 100 includes a step ofpeeling a support substrate as described later. A crack caused by thispeeling, which starts from an end portion of the substrate, can beeffectively stopped in a region where the semiconductor layer 110 isprovided.

As described above, by providing the semiconductor layer 110 to surroundthe display portion 102, cracks caused by the peeling step or thedivision step can be effectively prevented from developing into thedisplay portion 102.

In addition, the conductive layer 120, which is positioned on an innerside than the semiconductor layer 110 and provided to surround thedisplay portion 102, can prevent development of a crack that occurs inan end portion of the substrate when the display device 100 obtained bysubstrate division is bent. Accordingly, it is possible to improve thereliability of an electronic device in which the display device 100 isincorporated with a state where the display device 100 is bent or can bebent.

Note that in FIG. 1A and FIG. 2A, the semiconductor layer 110 and theconductive layer 120 surround the display portion 102, and form a closedcurve (a curve with no ends, or a loop) when seen from above. Inaddition, the opening formed over the semiconductor layer 110 surroundsthe display portion 102, is provided in and along a periphery of thesubstrate 101, and forms a closed curve (a curve with no ends, or aloop) when seen from above. The conductive layer 120 is not necessarilyprovided to form a closed curve and may be divided to form a dottedline. Furthermore, the conductive layer 120 may have a multiple linestructure (i.e., the conductive layer 120 may be formed of two or moreconductive layers). For example, in the case where the conductive layer120 has a double line structure (the conductive layer 120 is formed of afirst conductive layer and a second conductive layer), the structure ispreferably as follows: the first conductive layer (a dotted line) andthe second conductive layer (another dotted line) are placed inparallel; and an end of a part of the first conductive layer 120 a (adot of the dotted line) is not aligned with an end of a part of thesecond conductive layer (a dot of the other dotted line). This structurecan prevent development of a crack because a crack cannot developthrough spaces between the conductive layers.

In many cases, a crack is less likely to occur or develop in asemiconductor material used in the semiconductor layer 110 and a metalmaterial used in the conductive layer 120 than in an insulatingmaterial. Even when a crack occurs in an insulating layer under thesemiconductor layer 110 in an end portion of the substrate or aninsulating layer under the conductive layer 120 in the end portion ofthe substrate, the crack can be effectively stopped in a regionoverlapping with the semiconductor layer 110 or the conductive layer120.

FIGS. 3A and 3B are enlarged views in the vicinity of the semiconductorlayer 110. FIG. 3A shows the state before the substrate 101 is dividedand FIG. 3B shows the state after the substrate 101 is divided.

The openings provided in the insulating layer 138, the insulating layer134, and the insulating layer 135 are positioned on an inner side thanthe semiconductor layer 110. As shown by a region X denoted by thedotted line in FIGS. 3A and 3B, an end portion of the semiconductorlayer 110 is covered with these insulating layers.

Here, development of a crack is described. Considered is the case wherea component (with a single layer structure or a stacked structure) inwhich a crack occurs has two regions with different thicknesses, and atop surface of one region is positioned lower than a top surface of theother region (i.e., there is a step between the two regions). A cracktends to develop from the region having the higher top surface to theregion having the lower top surface. In contrast, a crack hardlydevelops from the region having the lower top surface to the regionhaving the higher top surface because the development of the crack isstopped by the step.

In the peeling step and the step of dividing the substrate 101, a crackin the display device 100 develops from an end portion of the substrateto the inner side (from the left to the light in FIGS. 3A and 3B). In aregion where the semiconductor layer 110 is provided, a step is formedby end portions of the insulating layers 138, 134, and 135. Accordingly,even when a crack occurs in the region where the semiconductor layer 110is provided, development of the crack is stopped by the step and thecrack is prevented from developing into a region where the insulatinglayer 135 and the like are provided.

As shown by a region Y, an end portion of the insulating layer 136 ispositioned on an inner side (on a closer side to the display portion102) than the end portions of the insulating layer 135 and the like. Theinsulating layer 136 and the insulating layer 135 and the like also forma step. Consequently, even when a crack occurs in the insulating layer135 and the like, this step can effectively stop development of thecrack.

Similarly, the conductive layer 120 is provided over the insulatinglayer 135 and an end portion of the conductive layer 120 forms a step,which can avoid development of a crack. The development of a crack canbe prevented more effectively particularly when two or more conductivelayers 120 are arranged in parallel as shown in FIGS. 3A and 3B andother drawings because a plurality of steps can be formed by thisstructure.

Note that in the display device 100, the semiconductor layer 110 and theconductive layer 120 are provided to surround not only the displayportion 102 but also the signal line driver circuit 103, the scan linedriver circuit 104, the external connection terminal 105, and the like.This structure can prevent a crack that occurs in an end portion of thesubstrate 101 from reaching the display portion 102, the signal linedriver circuit 103, the scan line driver circuit 104, and the externalconnection terminal 105; therefore, a malfunction of the display device100 can be prevented.

In terms of reducing formation steps, the semiconductor layer 110 ispreferably formed by processing the same semiconductor film as asemiconductor layer that forms a channel of a transistor. In addition,FIGS. 1A and 1B and FIGS. 2A and 2B illustrate the case where theconductive layer 120 is formed by processing the same conductive film asa pair of electrodes 133 in the transistor, but the present invention isnot limited to this structure. The conductive layer 120 may be formed byprocessing the same conductive film as another electrode (e.g., a gateelectrode 132) in the transistor, an electrode (e.g., a first electrode141) in a display element, another wiring, or the like.

Other components of the display device 100 are described below withreference to FIG. 1B.

The external connection terminal 105 is formed using the same materialas a conductive layer included in transistors or a light-emittingelement in the display device 100. In the structure in Embodiment 1, theexternal connection terminal 105 is formed using the same material as aconductive layer that forms a source electrode and a drain electrode ofthe transistor. By the external connection terminal 105 on which an FPCor an IC is mounted via an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like, a signal can be input.

FIG. 1B illustrates an example where a transistor 121 is included in thesignal line driver circuit 103. The signal line driver circuit 103 maybe, for example, a circuit in which an n-channel transistor and ap-channel transistor are used in combination, or a circuit that isformed of either n-channel transistors or p-channel transistors. Thesame applies to the scan line driver circuit 104. Although FIG. 1Billustrates an example of a driver-integrated structure in which thesignal line driver circuit 103 and the scan line driver circuit 104 areformed over an insulating surface over which the display portion 102 isformed, the present invention is not limited to this structure. Forexample, a driver circuit IC may be used as the signal line drivercircuit 103, the scan line driver circuit 104, or both and the drivercircuit IC may be mounted on the substrate 101 by a chip on glass (COG)method or a chip on film (COF) method; alternatively, a flexible printedsubstrate (FPC) provided with the driver circuit IC by the COF methodmay be mounted on the substrate 101.

FIG. 1B illustrates a cross-sectional structure of one pixel as anexample of the display portion 102. The pixel includes a switchingtransistor 123, a current control transistor 122, and the firstelectrode 141 electrically connected to one of the pair of electrodes133 in the current control transistor 122. An insulating layer 137 isprovided to cover a step of the first electrode 141. Under theinsulating layer 137, the insulating layer 136 is provided to covertransistors.

The transistors (e.g., 121, 122, and 123) in the display device 100 aretop-gate transistors. Each transistor includes a semiconductor layer 131that functions as a source region and a drain region and has an impurityregion; an insulating layer 138 that functions as a gate insulatinglayer; a gate electrode 132; the insulating layer 134 and the insulatinglayer 135 which are stacked to cover the gate electrode 132; and thepair of electrodes 133 electrically connected to the source region andthe drain region in the semiconductor layer 131 via an opening formed inthe insulating layer 134 and the insulating layer 135.

The light-emitting element 124 has a stacked structure in which thefirst electrode 141, an EL layer 142, and a second electrode 143 arestacked in this order over the insulating layer 136. Since the displaydevice 100 in Embodiment 1 is a top emission display device, alight-transmitting material is used for the second electrode 143. Areflective material is preferably used for the first electrode 141. TheEL layer 142 contains at least a light-emitting organic compound. Whenvoltage is applied between the first electrode 141 and the secondelectrode 143 with the EL layer 142 interposed therebetween so thatcurrent flows in the EL layer 142, whereby the light-emitting element124 can emit light.

A flexible substrate 130 is provided to face the substrate 101. Thesubstrate 101 and the substrate 130 are bonded with a bonding layer 114that is provided along the periphery of the substrate 130. A sealinglayer 113 is provided on an inner side than the bonding layer 114. Notethat a structure may be employed in which the substrate 101 and thesubstrate 130 are bonded with the sealing layer 113 without providingthe bonding layer 114.

On a surface of the substrate 130 facing the light-emitting element 124,a color filter 145 is provided in a region overlapping with thelight-emitting element 124 and a black matrix 146 is provided in aregion overlapping with the insulating layer 137. Between the substrate130 and each of the color filter 145 and the black matrix 146, aninsulating layer having a function of inhibiting entry of impurities maybe provided. On the other surface of the substrate 130 which does notface the light-emitting element 124, a transparent conductive film maybe provided to form a touch sensor, or a flexible substrate having afunction of a touch sensor may be attached.

[Material and Formation Method]

Materials and methods for forming the components described above aredescribed below.

[Flexible Substrate]

As a material for the flexible substrate, an organic resin, a glasssubstrate thin enough to have flexibility, or the like can be used.

Examples of such materials are polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, and a polyvinyl chloride resin. In particular, a materialwhose thermal expansion coefficient is low, for example, lower than orequal to 30×10⁻⁶/K is preferable, and a polyamide imide resin, apolyimide resin, or PET can be suitably used. A substrate in which afibrous body is impregnated with a resin (also referred to as prepreg)or a substrate whose thermal expansion coefficient is reduced by mixingan inorganic filler with an organic resin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples thereof include a polyvinyl alcoholbased fiber, a polyester based fiber, a polyamide based fiber, apolyethylene based fiber, an aramid based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As an exampleof the glass fiber, a glass fiber using E glass, S glass, D glass, Qglass, or the like can be given. These fibers may be used in a state ofa woven fabric or a nonwoven fabric, and a structure body in which thisfibrous body is impregnated with a resin and the resin is cured may beused as the flexible substrate. The structure body including the fibrousbody and the resin is preferably used as the flexible substrate, inwhich case the reliability against bending or breaking due to localpressure can be increased.

A material capable of transmitting light emitted from the EL layer 142is used for the flexible substrate through which light emitted from thelight-emitting element 124 is transmitted. To improve the outcouplingefficiency of the material provided on the light extraction side, therefractive index of the flexible, light-transmitting material ispreferably high. For example, a substrate obtained by dispersing aninorganic filler having a high refractive index into an organic resincan have a higher refractive index than the substrate formed of only theorganic resin. In particular, an inorganic filler having a particlediameter as small as 40 nm or less is preferably used, in which casesuch a filler can maintain optical transparency.

Since the substrate provided on the side opposite to the side throughwhich light is transmitted does not need to have a light-transmittingproperty, a metal substrate, an alloy substrate, or the like can be usedas well as the above substrates. To obtain flexibility and bendability,the thickness of a substrate is preferably greater than or equal to 10μm and less than or equal to 200 μm, more preferably greater than orequal to 20 μm and less than or equal to 50 μm. Although there is noparticular limitation on a material of the substrate, it is preferableto use, for example, aluminum, copper, nickel, a metal alloy such as analuminum alloy or stainless steel. A conductive substrate containing ametal or an alloy material is preferably used as the flexible substrateprovided on the side through which light is not transmitted, in whichcase heat dissipation of heat generated from the light-emitting element124 can be increased.

In the case where a conductive substrate is used, it is preferable touse a substrate subjected to insulation treatment in such a manner thata surface of the substrate is oxidized or an insulating film is formedover the surface of the substrate. For example, an insulating film maybe formed over the surface of the conductive substrate by anelectrodeposition method, a coating method such as a spin-coating methodor a dip method, a printing method such as a screen printing method, ora deposition method such as an evaporation method or a sputteringmethod. Alternatively, the surface of the substrate may be oxidized bybeing exposed to an oxygen atmosphere or heated in an oxygen atmosphereor by an anodic oxidation method.

In the case where the flexible substrate has an uneven surface, aplanarization layer may be provided to cover the uneven surface so thata flat insulating surface is formed. An insulating material can be usedfor the planarization layer; an organic material or an inorganicmaterial can be used. The planarization layer can be formed by adeposition method such as a sputtering method, a coating method such asa spin-coating method or a dip method, a discharging method such as anink-jet method or a dispensing method, a printing method such as ascreen printing method, or the like.

As the flexible substrate, a material in which a plurality of layers arestacked can also be used. For example, a material in which two or morekinds of layers formed of an organic resin are stacked, a material inwhich a layer formed of an organic resin and a layer formed of aninorganic material are stacked, or a material in which two or more kindsof layers formed of an inorganic material are stacked is used. With alayer formed of an inorganic material, moisture and the like areprevented from entering the inside, resulting in improved reliability ofthe display device.

As the inorganic material, an oxide material, a nitride material, or anoxynitride material of a metal or a semiconductor, or the like can beused. For example, silicon oxide, silicon nitride, silicon oxynitride,aluminum oxide, aluminum nitride, or aluminum oxynitride may be used.

For example, in the case where a layer formed of an organic resin and alayer formed of an inorganic material are stacked, the layer formed ofan inorganic material can be formed over or under the layer formed of anorganic resin by a sputtering method, a chemical vapor deposition (CVD)method, a coating method, or the like.

As the flexible substrate, a glass substrate thin enough to haveflexibility may also be used. Specifically, it is preferable to use asheet in which an organic resin layer, a bonding layer, and a glasslayer are sequentially stacked from the side close to the light-emittingelement 124. The thickness of the glass layer is greater than or equalto 20 μm and less than or equal to 200 μm, preferably greater than orequal to 25 μm and less than or equal to 100 μm. Such a thickness allowsthe glass layer to have both high flexibility and a high barrierproperty against water and oxygen. The thickness of the organic resinlayer is greater than or equal to 10 μm and less than or equal to 200μm, preferably greater than or equal to 20 μm and less than or equal to50 μm. With such an organic resin layer in contact with the glass layer,breakage or a crack of the glass layer can be inhibited, resulting inincreased mechanical strength. Forming the flexible substrate by usingsuch a composite material of a glass material and an organic resin makesit possible to obtain a flexible display device with extremely highreliability.

[Light-Emitting Element]

A material that transmits light emitted from the EL layer 142 is usedfor an electrode on the light emission side in the light-emittingelement 124.

As the light-transmitting material, indium oxide, indium oxide-tinoxide, indium oxide-zinc oxide, zinc oxide, and zinc oxide to whichgallium is added can be used. Graphene may also be used. Other examplesare a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, andtitanium; and an alloy material containing any of these metal materials.A nitride of the metal material (e.g., titanium nitride) or the like mayalso be used. In the case of using the metal material (or the nitridethereof), the thickness is set small enough to be able to transmitlight. Alternatively, a stack including any of the above materials canalso be used as the conductive layer. For example, a stacked filmincluding a silver-magnesium alloy and indium oxide-tin oxide ispreferably used, in which case electrical conductivity can be increased.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink-jet method, aprinting method such as a screen printing method, or a plating methodmay be used.

Note that when the above conductive oxide having a light-transmittingproperty is formed by a sputtering method, the use of a depositionatmosphere containing argon and oxygen allows the light-transmittingproperty to be increased.

Further, in the case where the conductive oxide film is formed over theEL layer, a first conductive oxide film formed under an atmospherecontaining argon with a reduced oxygen concentration and a secondconductive oxide film formed under an atmosphere containing argon andoxygen are preferably stacked, in which case film formation damage tothe EL layer can be reduced. In this case, in the formation of the firstconductive oxide film, it is preferable to use an argon gas with highpurity, for example, an argon gas whose dew point is lower than or equalto −70° C., more preferably lower than or equal to −100° C.

A material capable of reflecting light emitted from the EL layer 142 ispreferably used for the electrode provided on the side opposite to theside through which light is transmitted.

As the light-reflecting material, for example, a metal such as aluminum,gold, platinum, silver, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, or palladium or an alloy containing any of these metalscan be used. Alternatively, lanthanum, neodymium, germanium, or the likemay be added to a metal or an alloy containing the metal material. Inaddition, any of the following can be used: alloys containing aluminum(aluminum alloys) such as an alloy of aluminum and titanium, an alloy ofaluminum and nickel, and an alloy of aluminum and neodymium; and alloyscontaining silver such as an alloy of silver and copper, an alloy ofsilver, palladium, and copper, and an alloy of silver and magnesium. Analloy of silver and copper is preferable because of its high heatresistance. Further, by stacking a metal film or a metal oxide film incontact with an aluminum alloy film, oxidation of the aluminum alloyfilm can be suppressed. Examples of a material for the metal film or themetal oxide film are titanium and titanium oxide. Further alternatively,a stack including a film containing any of the above light-transmittingmaterials and a film containing any of the above metal materials may beused. For example, a stacked film including silver and indium oxide-tinoxide, a stacked film including a silver-magnesium alloy and indiumoxide-tin oxide, or the like can be used.

Such an electrode is formed by an evaporation method, a sputteringmethod, or the like. A discharging method such as an ink-jet method, aprinting method such as a screen printing method, or a plating methodmay be used.

The EL layer 142 includes at least a layer containing a light-emittingorganic compound (hereinafter also called a light-emitting layer), andmay be either a single layer or a stack including a plurality of layers.An example of the structure in which a plurality of layers is stacked isa structure in which a hole-injection layer, a hole-transport layer, alight-emitting layer, an electron-transport layer, and anelectron-injection layer are stacked in this order from an anode side.Note that not all of these layers except the light-emitting layer arenecessarily provided in the EL layer 142. Further, each of these layersmay be provided in duplicate or more. Specifically, in the EL layer 142,a plurality of light-emitting layers may overlap each other or anotherhole-injection layer may overlap the electron-injection layer.Furthermore, another component such as an electron-relay layer may beadded as appropriate as an intermediate layer, in addition to the chargegeneration layer. Alternatively, a plurality of light-emitting layersexhibiting different colors may be stacked. For example, a whiteemission can be obtained by stacking two or more layers emitting lightof complementary colors.

The EL layer 142 can be formed by a vacuum evaporation method, adischarging method such as an ink-jet method or a dispensing method, ora coating method such as a spin-coating method.

[Bonding Layer and Sealing Layer]

As the bonding layer and the sealing layer, it is possible to use, forexample, a gel or a curable material such as a two-component-mixturetype resin, a thermosetting resin, or a light curable resin. Forexample, an epoxy resin, an acrylic resin, a silicone resin, a phenolresin, polyimide, polyvinyl chloride (PVC), polyvinyl butyral (PVB), orethylene vinyl acetate (EVA) can be used. In particular, a material withlow moisture permeability, such as an epoxy resin, is preferable.

A drying agent may be contained in the bonding layer and the sealinglayer. For example, a substance that absorbs moisture by chemicaladsorption, such as oxide of an alkaline earth metal (e.g., calciumoxide or barium oxide), can be used.

Alternatively, a substance that adsorbs moisture by physical adsorption,such as zeolite or silica gel, may be used as the drying agent. In thecase where the drying agent is applied to a lighting device, when agranular drying agent is employed, light emitted from the light-emittingelement 124 is diffusely reflected by the drying agent; thus, a highlyreliable light-emitting device with improved viewing angle dependence,which is particularly useful for lighting and the like, can be achieved.

[Transistor]

There is no particular limitation on structures of transistors in thedisplay portion 102, the signal line driver circuit 103, and the scanline driver circuit 104. For example, a forward staggered transistor, aninverted staggered transistor, or the like may be used. Furthermore, atop-gate transistor or a bottom-gate transistor may be used. Inaddition, a channel-etched transistor or a channel protective transistormay be used. In the case of a channel protective transistor, a channelprotective film may be provided only over a channel region.Alternatively, an opening may be formed only in a portion where a sourceelectrode and a drain electrode are in contact with a semiconductorlayer and a channel protective film may be provided in an area otherthan the opening.

As a semiconductor applicable to a semiconductor layer in which achannel of a transistor is formed, for example, a semiconductor materialsuch as silicon or germanium, a compound semiconductor material, anorganic semiconductor material, or an oxide semiconductor material maybe used.

There is no particular limitation on the crystallinity of asemiconductor used for the transistors, and an amorphous semiconductoror a semiconductor having crystallinity (a microcrystallinesemiconductor, a polycrystalline semiconductor, a single crystalsemiconductor, or a semiconductor partly including crystal regions) maybe used. A semiconductor having crystallinity is preferably used, inwhich case deterioration of transistor characteristics can be reduced.

For example, in the case of using silicon as the semiconductor,amorphous silicon, microcrystalline silicon, polycrystalline silicon,single crystal silicon, or the like can be used.

In the case of using an oxide semiconductor as the semiconductor, anoxide semiconductor containing at least one of indium, gallium, and zincis preferably used. Typically, an In—Ga—Zn-based metal oxide can begiven. An oxide semiconductor having a wider band gap and a lowercarrier density than silicon is preferably used, in which case off-stateleakage current can be reduced.

The case of using a top-gate transistor is described in Embodiment 1,and the case of using a bottom-gate transistor is described inEmbodiment 2.

[Layer to be Peeled and Insulating Layer]

The layer 112 has a function of inhibiting diffusion of impuritiespassing through the substrate 101 and the bonding layer 111. The layer112 and the insulating layer 138, which are in contact with asemiconductor layer of a transistor, and the insulating layer 134 andthe insulating layer 135, which cover a transistor, preferably preventimpurities from diffusing into the semiconductor layer. These insulatinglayers can be formed using, for example, oxide or nitride of asemiconductor such as silicon or oxide or nitride of metal such asaluminum. Alternatively, a stacked film of such an inorganic insulatingmaterial or a stacked film of such an inorganic insulating material andan organic insulating material may be used.

As the inorganic insulating material, for example, a single layer of ora stack including one or more materials selected from aluminum nitride,aluminum oxide, aluminum nitride oxide, aluminum oxynitride, magnesiumoxide, gallium oxide, silicon nitride, silicon oxide, silicon nitrideoxide, silicon oxynitride, germanium oxide, zirconium oxide, lanthanumoxide, neodymium oxide, and tantalum oxide. In this specification, thenitride oxide refers to a material containing a larger amount ofnitrogen than oxygen, and the oxynitride refers to a material containinga larger amount of oxygen than nitrogen. The element content can bemeasured by, for example, RBS.

As the inorganic insulating material, a high-k material such as hafniumsilicate (HfSiO_(x)), hafnium silicate to which nitrogen is added(HfSi_(x)O_(y)N_(z)), hafnium aluminate to which nitrogen is added(HfAl_(x)O_(y)N_(z)), hafnium oxide, or yttrium oxide may be used.

The insulating layer 136 functions as a planarization layer coveringsteps formed due to a transistor, a wiring, or the like. For theinsulating layer 136, for example, an organic resin such as polyimide,acrylic, polyamide, or epoxy or an inorganic insulating material can beused. It is preferable to use a photosensitive resin (e.g., acrylic orpolyimide) for the insulating layer 136. The insulating layer 137 can beformed with the same material as the insulating layer 136.

[Color Filter and Black Matrix]

The color filter 145 is provided in order to adjust the color of lightemitted from the light-emitting element 124 to increase the colorpurity. For example, in a full-color display device using whitelight-emitting elements, a plurality of pixels provided with colorfilters of different colors are used. In that case, the color filtersmay be those of three colors of red (R), green (G), and blue (B) or fourcolors (yellow (Y) in addition to these three colors). Further, a white(W) pixel may be added to R, G, and B pixels (and a Y pixel). That is,color filters of four colors (or five colors) may be used.

The black matrix 146 is provided between the adjacent color filters 145.The black matrix 146 shields a pixel from light emitted from thelight-emitting element 124 in an adjacent pixel, thereby preventingcolor mixture between the adjacent pixels. When the color filter 145 isprovided so that its end portion overlaps the black matrix 146, lightleakage can be reduced. The black matrix 146 can be formed using amaterial that blocks light emitted from the light-emitting element 124,for example, a metal or an organic resin containing a pigment. Note thatthe black matrix 146 may be provided in a region other than the displayportion 102, for example, in the signal line driver circuit 103.

An overcoat may be formed to cover the color filter 145 and the blackmatrix 146. The overcoat protects the color filter 145 and the blackmatrix 146 and suppresses the diffusion of impurities included in thecolor filter 145 and the black matrix 146. The overcoat is formed usinga material that transmits light emitted from the light-emitting element124, and can be formed using, for example, an inorganic insulating filmor an organic insulating film.

An example where the display device has a top emission structure isdescribed here, but a bottom emission structure may be employed. In thecase of a bottom emission display device, the color filter 145 isprovided closer to the substrate 101 than the light-emitting element 124is. For example, the color filter 145 may be provided on the insulatinglayer 135 and the black matrix 146 may be provided to overlap with atransistor or the like.

Described in Embodiment 1 is a structure provided with a color filter,but a structure without using a color filter may be employed in whicheach pixel includes any one of light-emitting elements exhibiting lightof different colors (e.g., R, G, and B).

The above is the description of the components.

Although a display device using a light-emitting element as a displayelement is described in Embodiment 1, another display device (e.g., aliquid crystal display device using a liquid crystal element or anelectronic paper performing a display in an electrophoretic mode) may beemployed. The liquid crystal display device is described in Embodiment2.

[Example of Manufacturing Method]

An example of a method of manufacturing the display device 100 isdescribed below with reference to drawings. In particular, an example ofa method of manufacturing a plurality of display devices 100 from onesubstrate is described in Embodiment 1.

FIGS. 4A to 4D, FIGS. 5A to 5C, and FIGS. 6A and 6B are schematiccross-sectional views each illustrating a stage in a method ofmanufacturing the display device 100 described below. FIGS. 4A to 4D,FIGS. 5A to 5C, and FIG. 6A illustrate cross-sectional structures of thecomponents in FIGS. 2A and 2B. FIG. 6B illustrates a cross-sectionalstructure of the components in FIGS. 1A and 1B.

[Formation of Peeling Layer]

First, a peeling layer 152 is formed over a support substrate 151.

A substrate having resistance high enough to withstand at least heat ina later step is used as the support substrate 151. Examples of thesupport substrate 151 include a glass substrate, a resin substrate, asemiconductor substrate, a metal substrate, and a ceramic substrate.

Note that it is preferable to use a large glass substrate as the supportsubstrate 151 in terms of productivity. For example, a glass substratehaving any of the following sizes or a larger size can be used: the 3rdgeneration (550 mm×650 mm), the 3.5th generation (600 mm×720 mm or 620mm×750 mm), the 4th generation (680 mm×880 mm or 730 mm×920 mm), the 5thgeneration (1100 mm×1300 mm), the 6th generation (1500 mm×1850 mm), the7th generation (1870 mm×2200 mm), the 8th generation (2200 mm×2400 mm),the 9th generation (2400 mm×2800 mm or 2450 mm×3050 mm), and the 10thgeneration (2950 mm×3400 mm).

A high-melting-point metal such as tungsten, titanium, or molybdenum canbe used for the peeling layer 152. Tungsten is preferably used.

The peeling layer 152 can be formed by a sputtering method, for example.

[Formation of Layer to be Peeled]

Next, the layer 112 is formed over the peeling layer 152.

For the layer 112, an inorganic insulating material such as siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride, oraluminum oxide can be used. The layer 112 can be a single layer orstacked layers containing the above inorganic insulating material.

In particular, it is preferable that the layer 112 have a stackedstructure including two or more layers. In the stacked structure, atleast one of the layers is preferably a layer that releases hydrogenwhen heated, and the closest layer to the peeling layer 152 ispreferably a layer through which hydrogen passes. For example, the layer112 has a stacked structure including a layer containing siliconoxynitride and a layer containing silicon nitride in this order from thepeeling layer 152 side.

The layer 112 can be formed by a film formation method such as asputtering method or a plasma CVD method. In particular, the layer 112is preferably formed by a plasma CVD method using a deposition gascontaining hydrogen.

A surface of the peeling layer 152 is oxidized when the layer 112 isformed, and as a result, an oxide layer (not shown) is formed betweenthe peeling layer 152 and the layer 112. The oxide layer contains anoxide of the metal contained in the peeling layer 152. The oxide layerpreferably contains tungsten oxide.

Tungsten oxide is generally represented by WO_((3-x)) and is anon-stoichiometric compound which can have a variety of compositions,typically WO₃, W₂O₅, W₄O₁₁, and WO₂. Titanium oxide TiO_((2-x)) andmolybdenum oxide MoO_((3-x)) are also non-stoichiometric compounds.

The oxide layer at this stage preferably contains a large amount ofoxygen. For example, in the case where tungsten is used for the peelinglayer 152, the oxide layer is preferably a tungsten oxide layercontaining WO₃ as its main component.

The oxide layer can also be formed over the surface of peeling layer 152in advance by performing plasma treatment on the surface of the peelinglayer 152 in an atmosphere containing an oxidized gas (preferably adinitrogen monoxide gas) before the formation of the layer 112. Whensuch a method is employed, the thickness of the oxide layer can varydepending on the conditions for the plasma treatment and the thicknessof the oxide layer can be controlled more effectively than in the casewhere plasma treatment is not performed.

The thickness of the oxide layer is, for example, greater than or equalto 0.1 nm and less than or equal to 100 nm, preferably greater than orequal to 0.5 nm and less than or equal to 20 nm Note that the oxidelayer with an extremely small thickness cannot be observed in across-sectional image in some cases.

[Heat Treatment]

Next, heat treatment is performed to change the quality of the oxidelayer. By the heat treatment, hydrogen is released from the layer 112 tothe oxide layer.

The metal oxide in the oxide layer is reduced by hydrogen supplied tothe oxide layer, so that a plurality of regions with differentproportions of oxygen are mixed in the oxide layer. For example, in thecase where tungsten is used for the peeling layer 152, WO₃ in the oxidelayer is reduced to generate an oxide with proportion of oxygen lowerthan that of WO₃ (e.g., WO₂), resulting in a state where WO₃ and theoxide with the lower proportion of oxygen are mixed. The crystalstructure of such a metal oxide depends on the proportion of oxygen;thus, when a plurality of regions with different proportions of oxygenis provided in the oxide layer, the mechanical strength of the oxidelayer is reduced. As a result, the oxide layer is likely to be damagedinside, so that the peelability in a later peeling step can be improved.

The heat treatment may be performed at a temperature higher than orequal to the temperature at which hydrogen is released from the layer112 and lower than or equal to the temperature at which the supportsubstrate 151 is softened. Furthermore, the heat treatment is preferablyperformed at a temperature higher than or equal to the temperature atwhich a reduction reaction between hydrogen and the metal oxide in theoxide layer occurs. For example, in the case where tungsten is used forthe peeling layer 152, the heating temperature is higher than or equalto 420° C., higher than or equal to 450° C., higher than or equal to600° C., or higher than or equal to 650° C.

The higher the temperature of the heat treatment is, the more the amountof hydrogen released from the layer 112 can be, leading to improvedpeelability. However, even when the heating temperature is reduced inconsideration of the heat resistance of the support substrate 151 andthe productivity, high peelability can be achieved by forming the oxidelayer in advance by performing plasma treatment on the peeling layer 152as described above.

[Formation of Semiconductor Layer]

A semiconductor film is formed over the layer 112. A resist mask isformed over the semiconductor film by a photolithography process or thelike and unnecessary portions of the semiconductor film are etched. Theresist mask is removed; thus, the semiconductor layer 131 that forms atransistor and the semiconductor layer 110 are formed (FIG. 4B).

The semiconductor film is formed by an appropriate method depending on amaterial. For example, a sputtering method, a CVD method, an MBE method,an atomic layer deposition (ALD) method, or a pulsed laser deposition(PLD) method can be used.

In the case where a polycrystalline silicon semiconductor film is usedas the semiconductor film, a film of amorphous silicon is deposited andsubjected to crystallization (e.g., laser light irradiation or heattreatment) to form a semiconductor film including polycrystallinesilicon.

[Formation of Gate Insulating Layer]

The insulating layer 138 is formed to cover the semiconductor layer 110and the semiconductor layer 131.

The insulating layer 138 can be formed by a plasma CVD method, asputtering method, or the like.

[Formation of Gate Electrode]

A conductive film is formed over the insulating layer 138. A resist maskis formed over the conductive film by a photolithography process or thelike and unnecessary portions of the conductive film are etched. Theresist mask is removed; thus, the gate electrode 132 is formed.

At this time, wirings and the like which form a circuit may be formedsimultaneously.

The conductive film to be the gate electrode 132 may be formed by asputtering method, an evaporation method, a CVD method, or the like.

[Formation of Impurity Region]

An impurity is added to a region in the semiconductor layer 131 thatforms a transistor, where the semiconductor layer 131 does not overlapwith the gate electrode 132. As the dopant, an n-type dopant such asphosphorus or arsenic or a p-type dopant such as boron or aluminum canbe used.

[Formation of Insulating Layer]

The insulating layer 134 and the insulating layer 135 are formed tocover the insulating layer 138 and the gate electrode 132.

The insulating layer 134 and the insulating layer 135 can be formed by aplasma CVD method, a sputtering method, or the like.

An insulating layer over the gate electrode 132 having a stackedstructure of two layers (the insulating layers 134 and 135) is describedin Embodiment 1, but the present invention is not limited to thisstructure. The insulating layer may have a single layer structure or astacked structure of three or more layers.

[Formation of Opening]

An opening reaching the impurity region in the semiconductor layer 131is formed in the insulating layers 138, 134, and 135. At this time, anopening that exposes part of a top surface of the semiconductor layer110 is also formed in the insulating layers 138, 134, and 135 over thesemiconductor layer 110 (FIG. 4C).

A resist mask is formed over the insulating layer 135 by aphotolithography process or the like, and unnecessary portions of theinsulating layers 138, 134, and 135 are etched. The resist mask isremoved; thus, the openings are formed.

Since the semiconductor layer 110 is provided, the opening over thesemiconductor layer 110 can be formed when the opening over thesemiconductor layer 131 of the transistor is formed. In the case wherethe semiconductor layer 110 is not provided, for example, the layer 112is also etched in the opening formation, and the opening reaches thepeeling layer 152 in some cases. If a surface of the peeling layer 152is exposed, film peeling might occur from the exposed portion. Thus, thesemiconductor layer 110 has a function of an etching stopper for formingan opening in a stable manner.

[Formation of Source Electrode, Drain Electrode, and Conductive Layer]

A conductive film is formed over the above openings and the insulatinglayer 135. A resist mask is formed over the conductive film by aphotolithography process or the like and unnecessary portions of theconductive film are etched. The resist mask is removed; thus, theelectrodes 133 that function as a source electrode and a drain electrodeof the transistor and the conductive layer 120 are formed (FIG. 4D).

At this time, wirings and the like which form a circuit may be formedsimultaneously.

The conductive film is formed by a sputtering method, an evaporationmethod, a CVD method, or the like.

In FIG. 4D and other drawings, two conductive layers 120 are provided.One conductive layer 120 may be provided, but development of a crack canbe effectively avoided when a plurality of conductive layers 120 isarranged in parallel with a gap as illustrated in FIG. 4D.

At this point, the transistors 121, 122, and 123 are completed.

[Formation of Insulating Layer]

The insulating layer 136 that functions as a planarization layer isformed. At this time, an opening reaching one of the electrodes 133 ofthe current control transistor 122, an opening reaching thesemiconductor layer 110, and an opening reaching a wiring to be theexternal connection terminal 105 are formed in the insulating layer 136.

For example, the insulating layer 136 is preferably formed in such amanner that a photosensitive organic resin is applied by a spin coatingmethod or the like, and then is subjected to selective light exposureand development. As another formation method, a sputtering method, anevaporation method, a droplet discharging method (e.g., an inkjetmethod), a printing method (e.g., a screen printing method or an offsetprinting method), or the like may be used.

[Formation of First Electrode]

A conductive film is formed over the insulating layer 136. A resist maskis formed over the conductive film by a photolithography process and anunnecessary portion of the conductive film is etched. The resist mask isremoved; thus, the first electrode 141 electrically connected to one ofthe electrodes 133 of the transistor is formed.

At this time, wirings and the like which form a circuit may be formedsimultaneously.

The conductive film is formed by a sputtering method, an evaporationmethod, a CVD method, or the like.

[Formation of Insulating Layer]

The insulating layer 137 covering an end portion of the first electrode141 is formed (FIG. 5A). At this time, an opening reaching thesemiconductor layer 110 and an opening reaching the wiring to be theexternal connection terminal 105 are formed in the insulating layer 137.

For example, the insulating layer 137 is preferably formed in such amanner that a photosensitive organic resin is applied by a spin coatingmethod or the like, and then is subjected to selective light exposureand development. As another formation method, a sputtering method, anevaporation method, a droplet discharging method (e.g., an inkjetmethod), a printing method (e.g., a screen printing method or an offsetprinting method), or the like may be used.

[Peeling]

Peeling is performed between the peeling layer 152 and the layer 112(FIG. 5B).

For the peeling, for example, the support substrate 151 is fixed to asuction stage and a peeling starting point is formed between the peelinglayer 152 and the layer 112. The peeling starting point may be formedby, for example, inserting a sharp instrument such as a knife betweenthe layers. Alternatively, the peeling starting point may be formed byirradiating part of the peeling layer 152 with laser light to melt,evaporate, or thermally break the part of the peeling layer 152. Furtheralternatively, the peeling starting point may be formed by drippingliquid (e.g., alcohol, water, or water containing carbon dioxide) ontoan end portion of the peeling layer 152 so that the liquid penetratesinto an interface between the peeling layer 152 and the layer 112 byusing capillary action.

Then, physical force is gently applied to the area where the peelingstarting point is formed in a direction substantially perpendicular tothe bonded surfaces, so that peeling can be caused without damage to thelayer 112 and layers provided thereover.

To protect components formed over the layer 112, such as a transistor,in the peeling step, it is preferable that a flexible base material orthe like be attached to the layer 112 with a bonding layer (e.g., awater-soluble adhesive or a low-viscosity adhesive) that can be removed.

For example, peeling may be caused by attaching tape or the like to thesupport substrate 151 or the base material and pulling the tape in theaforementioned direction. Alternatively, peeling may be caused bypulling an end portion of the support substrate 151 or the base materialwith a hook-like member. Further alternatively, peeling may be caused bypulling an adhesive member or a member capable of vacuum suctionattached to the back side of the support substrate 151 or the basematerial. Still further alternatively, peeling may be caused by pressingan adhesive roller to the back side of the support substrate 151 or thebase material and rolling and moving the roller relatively.

Here, peeling is performed in such a manner that liquid containing watersuch as water or an aqueous solution is added to the peeling interfaceand the liquid penetrates into the peeling interface, so that thepeelability can be improved.

Peeling mainly occurs in an oxide layer formed between the peeling layer152 and the layer 112 or at an interface between the oxide layer and thepeeling layer 152. Thus, after the peeling, the oxide layer is attachedto a surface of the peeling layer 152 and a surface of the layer 112 insome cases. Since peeling is likely to occur at the interface betweenthe oxide layer and the peeling layer 152 as described above, thethickness of the oxide layer attached to the layer 112 is larger thanthat of the oxide layer attached to the peeling layer 152 in many cases.

It is preferable that a peeling starting point be formed in an endportion of the support substrate 151 so that the peeling proceeds fromthe end portion. In formation of the peeling starting point, a crackoccurs in some cases in the insulating layer over the layer 112 near theend portion of the support substrate 151. The crack formed at this timemight develop from the outer side to the inner side of the supportsubstrate 151, as the peeling proceeds. However, even when such a crackoccurs, development of the crack can be stopped in a region where thesemiconductor layer 110 surrounding the display portion 102 is provided;thus, the crack can be effectively prevented from reaching the displayportion 102.

[Bonding]

The flexible substrate 101 is bonded to the surface of the layer 112 onwhich peeling has been performed, with the bonding layer 111 interposedtherebetween.

In the case where before the peeling, a flexible base material isattached to the layer 112 with a bonding layer that can be removed, theflexible base material and the bonding layer are removed at this step.

[Formation of Light-Emitting Element]

The EL layer 142 and the second electrode 143 are sequentially formedover the first electrode 141; thus the light-emitting element 124 isformed (FIG. 5C).

Through the above steps, a plurality of transistors and thelight-emitting element 124 can be provided over the flexible substrate101.

[Bonding]

The substrate 130 provided with the color filter 145 and the blackmatrix 146 is prepared.

The color filter 145 and the black matrix 146 can be formed on theflexible substrate 130 in a manner similar to that of the insulatinglayer 136 and the insulating layer 137. The color filter 145 and theblack matrix 146 may be formed directly on the flexible substrate 130.Alternatively, the color filter 145 and the black matrix 146 may beformed over the flexible substrate 130 using the aforementioned peelingmethod: a peeling layer and a layer to be peeled are formed over asupport substrate, the color filter 145 and the black matrix 146 areformed over the layer to be peeled, the support substrate and thepeeling layer are separated from the layer to be peeled and the othercomponents (including the color filter 145 and the black matrix 146),and the layer to be peeled is bonded to the flexible substrate 130 witha bonding layer.

A bonding layer 114 is formed over the substrate 130 or the substrate101.

A curable resin is applied by, for example, a discharging method such asa dispensing method or a printing method such as a screen printingmethod, and a solvent in the resin is vaporized; thus, the bonding layer114 is formed.

The sealing layer 113 is formed on an inner side than the bonding layer114, over the substrate 130 or the substrate 101. The sealing layer 113can be formed by a method similar to that of the bonding layer 114.

The bonding layer 114 functions as a partition wall (also referred to asbank or barrier) that prevents the sealing layer 113 from spreading to aregion where the external connection terminal 105 or the semiconductorlayer 110 is provided. When there is no possibility that the sealinglayer 113 spreads to the region where the external connection terminal105 or the semiconductor layer 110 is provided in view of a material ora formation method of the sealing layer 113 or a region where thesealing layer 113 is provided, the bonding layer 114 is not necessarilyprovided.

The substrate 130 is attached to the substrate 101, and the bondinglayer 114 and the sealing layer 113 are cured, whereby the substrate 130is bonded to the substrate 101 (FIG. 6A).

At this time, if the substrate 130 that is cut out in an appropriatesize is bonded to each of the display devices 100 formed over thesubstrate 101, the process becomes complicated and the productivitydecreases. For this reason, it is preferable to perform the followingsas illustrated in FIG. 6A: a substrate having about the same size as thesubstrate 101 is used as the substrate 130; the substrate 130 isattached to the substrate 101 so as to cover the plurality of displaydevices 100; and the substrate 130 and the substrate 101 are cut so thatthe plurality of display devices 100 is separated into individualdevices.

[Division]

The substrate 101 and the substrate 130 are cut so that the plurality ofdisplay devices 100 is separated into individual devices (FIG. 6B).

For cutting the substrate 101 and the substrate 130, a cutter knife witha sharp blade, a scriber, or a laser cutter can be used. In the casewhere the substrate 101 and the substrate 130 are cut in the sameposition, a shearing machine may be used, for example.

The substrate 101 is cut along the openings formed in the insulatinglayers (134, 135, 136, 137, and 138) over the semiconductor layer 110.

The substrate 130 is cut in a region on an inner side than at least theexternal connection terminal 105 not to overlap with the externalconnection terminal 105. Note that the substrate 130 in a region wherethe external connection terminal 105 is not provided may be cut in thesame positions as the substrate 101.

Through the above steps, the display device 100 can be manufactured.

Note that the case where a metal material is used for the peeling layerand an inorganic insulating material is used for the layer to be peeledis described in the above manufacturing method, but a combination of thematerials of the peeling layer and the layer to be peeled is not limitedthereto. Materials of the peeling layer and the layer to be peeled areselected such that peeling is performed at an interface between thepeeling layer and the layer to be peeled or in the peeling layer. Forexample, a combination of low adhesive materials (e.g., a metal and aresin) may be employed.

The peeling layer is not necessary in the case where peeling can occurat an interface between the support substrate and the layer to bepeeled. For example, glass is used as the support substrate, an organicresin such as polyimide is used as the layer to be peeled, and peelingis performed by heating the organic resin. Alternatively, a metal layermay be provided between the support substrate and the layer to be peeledformed of an organic resin, and peeling may be performed at theinterface between the metal layer and the layer to be peeled formed ofan organic resin by heating the metal layer by feeding a current to themetal layer.

The case where the EL layer 142 and the second electrode 143 are formedafter the peeling is described in the above manufacturing method, butthe EL layer 142 and the second electrode 143 may be formed before thepeeling.

When the EL layer 142 is formed by a vacuum evaporation method, it mightbe difficult to form the EL layer 142 stably over an extremely largesubstrate because of bending of the substrate or the like. In such acase, the substrate is preferably divided into pieces with desired sizesbefore formation of the EL layer 142. At this time, it is preferablethat the substrate be not divided into small pieces each including onedisplay device 100, but be divided into pieces each including aplurality of display devices 100, and evaporation be performedsimultaneously to the plurality of display devices 100.

In the case where the substrate division is performed in two steps(substrate division before formation of the EL layer 142 and substratedivision for separating the plurality of display devices 100 intoindividual display device 100), it is preferable to form thesemiconductor layer 110 along division lines for the respective steps.For example, the semiconductor layer 110 that surrounds each displaydevice 100 and the semiconductor layer 110 that surrounds a regionincluding the plurality of display devices 100 are doubly provided.

By the above manufacturing method, flexible devices with fewer defectscaused by a crack can be manufactured with high productivity.

This embodiment can be combined with any of the other embodiments andexamples described in this specification as appropriate.

Embodiment 2

In this embodiment, a structure of a display device that differs fromthe display device shown in Embodiment 1 is described as an example.Note that description of the portions described in Embodiment 1 isomitted.

[Structural Example]

An example of a structure of an image display device in which a liquidcrystal element is used as a display element is described below.

FIG. 7 is a schematic cross-sectional view of a display device 200. Thedisplay device 200 differs from the display device 100 described inEmbodiment 1 mainly in that a liquid crystal element is used as adisplay element and a transistor has a different structure.

The display portion 102 includes a liquid crystal element 224 using anin-plane switching (IPS) mode. In the liquid crystal element 224, theorientation of a liquid crystal is controlled by an electric fieldgenerated in a direction parallel to the substrate surface.

A pixel includes at least one switching transistor 222 and a storagecapacitor that is not illustrated. A comb-shaped second electrode 243and a comb-shaped first electrode 241 electrically connected to one of asource electrode and a drain electrode of the transistor 222 areprovided apart from each other over the insulating layer 136.

For at least one of the first electrode 241 and the second electrode243, any of the above-described light-transmitting conductive materialsis used. It is preferable to use a light-transmitting conductivematerial for both of these electrodes because the aperture ratio of thepixel can be increased.

Although the first electrode 241 and the second electrode 243 aredistinguished from each other in FIG. 7 by using different hatchpatterns, these electrode layers are preferably formed by processing thesame conductive film.

A color filter 245 is provided at a position overlapping with the firstelectrode 241 and the second electrode 243. The color filter 245 isprovided over the insulating layer 135 in FIG. 7, but the position ofthe color filter is not limited to this position.

A liquid crystal 242 is provided between the substrate 130 and each ofthe first electrode 241 and the second electrode 243. An image can bedisplayed in the following way: an electric field is generated in thehorizontal direction by application of voltage between the firstelectrode 241 and the second electrode 243, orientation of the liquidcrystal 242 is controlled by the electric field, and polarization oflight from a backlight provided outside the display device is controlledin each pixel.

It is preferable to provide alignment films for controlling theorientation of the liquid crystal 242 on surfaces in contact with theliquid crystal 242. A light-transmitting material is used for thealignment films. Although not illustrated here, polarizing plates areprovided on an outside surface of the substrate 101 and an outsidesurface of the substrate 130 with respect to the liquid crystal element224.

As the liquid crystal 242, a thermotropic liquid crystal, alow-molecular liquid crystal, a high-molecular liquid crystal, aferroelectric liquid crystal, an anti-ferroelectric liquid crystal, orthe like can be used. Moreover, a liquid crystal exhibiting a blue phaseis preferably used, in which case an alignment film is not needed and awide viewing angle can be obtained.

A high-viscosity and low-fluidity material is preferably used for theliquid crystal 242.

Although the liquid crystal element 224 using IPS mode is described hereas an example, the mode of the liquid crystal element is not limited tothis, and a twisted nematic (TN) mode, a fringe field switching (FFS)mode, an axially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, or the likecan be used.

Transistors (e.g., a transistor 221 and the transistor 222) provided inthe display device 200 are bottom-gate transistors. Each of thetransistors includes a gate electrode 232, an insulating layer 238functioning as a gate insulating layer, a semiconductor layer 231, and apair of electrodes 233. In addition, the insulating layers 134, 135, and136 are provided to cover the transistors.

The semiconductor layer 110 illustrated in FIG. 7 is formed byprocessing the same film as the semiconductor layer 231 of thetransistor. A structure of the transistor in the display device 200 isdifferent from the structure of the transistor in the display device 100described in Embodiment 1, and a stacked structure around thesemiconductor layer 110 and the conductive layer 120 is different fromthat in the display device 100.

Specifically, the semiconductor layer 110 is formed over the insulatinglayer 238 functioning as a gate insulating layer, and the end portion ofthe semiconductor layer 110 is covered with the insulating layers 134and 135. The conductive layer 120 is provided over the insulating layer238, and the insulating layers 134 and 135 are provided over theconductive layer 120.

The above is the description on the example of the structure ofEmbodiment 2.

Note that the bottom-gate transistor described here can be replaced withthe top-gate transistor described in Embodiment 1. Alternatively, thetransistor described in Embodiment 1 can be replaced with thebottom-gate transistor described here. The stacked structure around thesemiconductor layer 110 and the conductive layer 120 inevitably changesin accordance with the structure of the transistor.

This embodiment can be combined with any of the other embodiments andexamples described in this specification as appropriate.

Embodiment 3

In this embodiment, electronic devices each including a display deviceare described as examples of a semiconductor device of one embodiment ofthe present invention.

The display device of one embodiment of the present invention has abendable display surface. Examples of such a display device include atelevision set (also referred to as television or television receiver),a monitor of a computer, a camera such as a digital camera or a digitalvideo camera, a digital photo frame, a mobile phone set (also referredto as mobile phone or mobile phone device), a portable game machine, aportable information terminal, an audio reproducing device, and a largegame machine such as a pachinko machine. In addition, a lighting deviceor a display device can be incorporated along a curved inside/outsidewall surface of a house or a building or a curved interior/exteriorsurface of a car. In addition, a lighting device or a display device canbe incorporated along a curved inside/outside wall surface of a house ora building or a curved interior/exterior surface of a car.

FIG. 8A illustrates an example of a mobile phone. A mobile phone 7100includes a display portion 7102 incorporated in a housing 7101,operation buttons 7103, an external connection port 7104, a speaker7105, a microphone 7106, a camera 7107, and the like. Note that themobile phone 7100 is manufactured using the display device of oneembodiment of the present invention for the display portion 7102.

When the display portion 7102 of the mobile phone 7100 illustrated inFIG. 8A is touched with a finger or the like, data can be input to themobile phone 7100. Operations such as making a call and entering acharacter can be performed by touch on the display portion 7102 with afinger or the like. For example, by touching an icon 7108 displayed onthe display portion 7102, application can be started.

The power can be turned on or off with the operation buttons 7103. Inaddition, types of images displayed on the display portion 7102 can beswitched; for example, switching images from a mail creation screen to amain menu screen.

Here, the display portion 7102 includes the display device of oneembodiment of the present invention. Thus, images can be displayed onthe bent display surface, and the mobile phone can have highreliability.

FIG. 8B is an example of a wristband-type display device. A portabledisplay device 7200 includes a housing 7201, a display portion 7202, anoperation button 7203, and a sending and receiving device 7204.

The portable display device 7200 can receive a video signal with thesending and receiving device 7204 and can display the received video onthe display portion 7202. In addition, with the sending and receivingdevice 7204, the portable display device 7200 can send an audio signalto another receiving device.

With the operation button 7203, power ON/OFF, switching of displayedvideos, adjusting volume, and the like can be performed.

Here, the display portion 7202 includes the display device of oneembodiment of the present invention. Thus, the portable display devicecan have a curved display portion and high reliability.

FIG. 8C illustrates an example of a wrist-watch-type portableinformation terminal A portable information terminal 7300 includes ahousing 7301, a display portion 7302, a band 7303, a buckle 7304, anoperation button 7305, an input output terminal 7306, and the like.

The portable information terminal 7300 is capable of executing a varietyof applications such as mobile phone calls, e-mailing, viewing andediting texts, music reproduction, Internet communication, and acomputer game.

The display surface of the display portion 7302 is bent, and images canbe displayed on the bent display surface. The display portion 7302includes a touch sensor, and operation control can be performed bytouching the screen with a finger, a stylus, or the like. For example,by touching an icon 7307 displayed on the display portion 7302,application can be started.

With the operation button 7305, a variety of functions such as timesetting, power ON/OFF, ON/OFF of wireless communication, setting andcancellation of manner mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation button 7305 can be set freely by setting the operation systemincorporated in the portable information terminal 7300.

The portable information terminal 7300 can employ near fieldcommunication that is a communication method in accordance with anexisting communication standard. For example, mutual communicationbetween the portable information terminal 7300 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible.

The portable information terminal 7300 includes the input outputterminal 7306, and data can be directly transmitted to and received fromanother information terminal via a connector. Power charging through theinput output terminal 7306 is possible. Note that the charging operationmay be performed by wireless power feeding without using the inputoutput terminal 7306.

The display device of one embodiment of the present invention can beused in the display portion 7302 of the portable information terminal7300.

The display device of one embodiment of the present invention can beused in any of the display portions of the electronic devices describedin this embodiment. Accordingly, a highly reliable electronic devicethat can display images on a curved surface and has fewer defects due tobending can be achieved.

This embodiment can be combined with any of the other embodiments andexamples described in this specification as appropriate.

Example

In this example, a semiconductor layer and a conductive layer, each ofwhich is one embodiment of the present invention, were formed over aflexible substrate, and a crack was observed before and after thesubstrate is divided. The results are described below.

[Fabrication of Sample]

First, an approximately 200-nm-thick silicon oxynitride film was formedover a glass substrate functioning as a support substrate by a plasmaCVD method. Next, an approximately 50-nm-thick tungsten film was formedas a peeling layer by a sputtering method. Then, an approximately600-nm-thick silicon oxynitride film, an approximately 200-nm-thicksilicon nitride film, an approximately 200-nm-thick silicon oxynitridefilm, an approximately 140-nm-thick silicon nitride oxide film, and anapproximately 100-nm-thick silicon oxynitride film were successivelyformed by a plasma CVD method as a layer to be peeled (hereinafterreferred to as layer).

An approximately 50-nm-thick polysilicon film was formed over the layer,and unnecessary portions were etched, whereby a semiconductor layer of atransistor and a semiconductor layer that surrounds the transistor wereformed. To form the polysilicon film, an amorphous silicon film wasformed by a plasma CVD method, solid-phase growth using Ni as acatalytic element was performed on the amorphous silicon film, and thecatalytic element that remained in the film was removed.

Next, an approximately 110-nm-thick silicon oxynitride film was formedas a gate insulating layer by a plasma CVD method. Then, anapproximately 30-nm-thick tantalum nitride film and an approximately370-nm-thick tungsten film were formed, and unnecessary portions wereetched, whereby a gate electrode was formed. An approximately50-nm-thick silicon oxynitride film, an approximately 140-nm-thicksilicon nitride oxide film, and an approximately 520-nm-thick siliconoxynitride film were formed as an interlayer insulating layer. Afterthat, the gate insulating layer and the interlayer insulating layer werepartly etched to form an opening such that an end portion of thesemiconductor layer was covered and part of the semiconductor layer wasexposed. Note that the insulating layers where the opening was formedare collectively called a first insulating layer.

An approximately 100-nm-thick titanium film, an approximately700-nm-thick aluminum film, and an approximately 100-nm-thick titaniumfilm were formed over the interlayer insulating layer by a sputteringmethod, and unnecessary portions were etched, whereby a pair ofelectrodes of the transistor and a conductive layer that surrounds thetransistor were formed.

An approximately 150-nm-thick silicon oxynitride film was formed, and anopening was formed over the semiconductor layer in a manner similar tothe above-described manner. Next, an approximately 2.0-μm-thickpolyimide film was formed by a photolithography process such that anopening was formed over the semiconductor layer. Then, an approximately50-nm-thick indium-tin oxide film was formed by a sputtering method andunnecessary portions were etched to form a first electrode. After that,an approximately 1.5-μm-thick polyimide film was formed by aphotolithography process such that an opening was formed over thesemiconductor layer. Note that the silicon oxynitride film and thetwo-layered polyimide film which were formed over the conductive layerare collectively called as a second insulating layer.

Next, a water-soluble resin was applied and cured. A UV-peeling tapewhose adhesion is weakened by ultraviolet light irradiation wasattached, the UV-peeling tape side was held by a suction stage, and thelayer was separated from the support substrate. A curable epoxy resinwas applied onto a surface of the layer on which peeling had beenperformed, and a 125-μm-thick polyimide film was attached thereto as asubstrate. After that, the UV-peeling tape was peeled and then thewater-soluble resin was removed.

Through the above steps, a sample including, over a flexible substrate,a transistor; a conductive layer surrounding a region where thetransistor is formed; and a semiconductor layer positioned on an outerside than the conductive layer was fabricated.

[Observation of Crack]

Before and after the substrate division, the vicinity of thesemiconductor layer and the conductive layer was observed with anoptical microscope.

FIGS. 9A to 12A are optical micrographs. A schematic cross-sectionalstructure (FIGS. 9B to 12B) of the observed portion is shown below eachoptical micrograph.

FIG. 9A is an optical micrograph taken before the substrate division.The left side shows a region where the semiconductor layer is exposed,and a crack occurs in this region. This crack is not developed into aninner side (the right side) than an end portion of the first insulatinglayer which overlaps with the semiconductor layer.

FIG. 10A and FIG. 11A are each an optical micrograph taken when thesubstrate is cut in a region where an opening overlaps with thesemiconductor layer. In each of the optical micrographs, a crackdevelops from the cut portion of the substrate (on the left side in themicrograph) into an inner side. In addition, as in FIG. 9A, thedevelopment of the crack is stopped at an end portion of the firstinsulating layer which overlaps with the semiconductor layer.

FIG. 12A is an optical micrograph taken after the substrate division.The portion in FIG. 12A is apart from the portions in FIGS. 9A to 11A. Acrack occurs in a region where the second insulating layer overlaps withthe first insulating layer (the left side in the micrograph). Thedevelopment of this crack is stopped at an end portion of the conductivelayer, and the crack does not develop into an inner side than the endportion.

The above results indicate that development of a crack can beeffectively stopped by providing a semiconductor layer, whose endportion is covered with an insulating layer, along the periphery of thesubstrate. Moreover, the development of a crack can be more effectivelystopped by providing a conductive layer on an inner side than thesemiconductor layer.

This application is based on Japanese Patent Application serial no.2013-081897 filed with Japan Patent Office on Apr. 10, 2013, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a flexiblesubstrate; a semiconductor element over the flexible substrate; asemiconductor layer over the flexible substrate and along a periphery ofthe flexible substrate; and an insulating layer over the semiconductorelement and the semiconductor layer, wherein the insulating layercomprises an opening over the semiconductor layer and along theperiphery of the flexible substrate, wherein a first end portion of thesemiconductor layer is covered with the insulating layer, wherein asecond end portion of the semiconductor layer is exposed in the opening,wherein an end portion of the flexible substrate is substantiallyaligned with the second end portion of the semiconductor layer, andwherein the semiconductor layer and the opening surround thesemiconductor element.
 2. The semiconductor device according to claim 1,wherein an end portion of the insulating layer is positioned over thesemiconductor layer.
 3. The semiconductor device according to claim 1,wherein each of the semiconductor layer and the opening has a shape of aclosed curve.
 4. The semiconductor device according to claim 1, furthercomprising a bonding layer and a layer containing an insulatingmaterial, wherein the bonding layer and the layer containing theinsulating material are positioned between the flexible substrate andthe semiconductor layer.
 5. The semiconductor device according to claim1, wherein the semiconductor element comprises a transistor.
 6. Thesemiconductor device according to claim 5, wherein the semiconductorlayer comprises the same material as a semiconductor in a channel of thetransistor.
 7. A semiconductor device comprising: a flexible substrate;a semiconductor element over the flexible substrate; a semiconductorlayer over the flexible substrate and along a periphery of the flexiblesubstrate; an insulating layer over the semiconductor element and thesemiconductor layer; and a conductive layer between the semiconductorelement and the semiconductor layer, wherein the insulating layercomprises an opening over the semiconductor layer and along theperiphery of the flexible substrate, wherein a first end portion of thesemiconductor layer is covered with the insulating layer, wherein asecond end portion of the semiconductor layer is exposed in the opening,wherein an end portion of the flexible substrate is substantiallyaligned with the second end portion of the semiconductor layer, andwherein the semiconductor layer, the opening, and the conductive layersurround the semiconductor element.
 8. The semiconductor deviceaccording to claim 7, wherein an end portion of the insulating layer ispositioned over the semiconductor layer.
 9. The semiconductor deviceaccording to claim 7, wherein each of the semiconductor layer and theopening has a shape of a closed curve.
 10. The semiconductor deviceaccording to claim 7, further comprising a bonding layer and a layercontaining an insulating material, wherein the bonding layer and thelayer containing the insulating material are positioned between theflexible substrate and the semiconductor layer.
 11. The semiconductordevice according to claim 7, wherein the semiconductor element comprisesa transistor.
 12. The semiconductor device according to claim 11,wherein the semiconductor layer comprises the same material as asemiconductor in a channel of the transistor.
 13. The semiconductordevice according to claim 11, wherein the conductive layer comprises thesame material as a gate electrode, a source electrode, or a drainelectrode of the transistor.